In general, a direct current motor with brushes is often used as an electric motor mounted in a vehicle such as an automobile. This type of direct current motor is constituted such that permanent magnets of two or four poles are arranged at the inner circumferential surface of a cylindrical yoke housing and an armature on which an armature coil is wound is arranged on the inner surface of this permanent magnet so as to freely rotate. As the permanent magnet, a sintered ferrite magnet formed in the shape of a tile is used in many cases. The armature has an armature core that is externally fitted and fixed on the rotating shaft, and a plurality of slots that are long in the axial direction are formed in the armature core.
Winding wire is singly wound at a predetermined interval in these slots to form a plurality of coils. Each coil is conducted to a segment that is attached to a rotating shaft.
Each segment is capable of making sliding contact with a pair of brushes that are supported in brush holders that are housed in a yoke housing. Then, when direct current is supplied to the coil via these brushes, the rotating shaft is rotated by the magnetic attraction and repulsion that are produced between the magnetic field formed in the armature core and the permanent magnets. The segments at which the brushes make sliding contact change in turn by this rotation, the direction of the current that flows to the coil is switched, so-called rectification is performed, and the armature core continuously rotates.
In recent years, with the increasing performance of automobiles, smaller size and higher output are required of direct current motors. Therefore, a direct current motor has been proposed that adopts an anisotropic rare earth bond magnet that is formed in a hollow cylindrical shape as the permanent magnet and this anisotropic rare earth bond magnet is magnetized to at least four poles. By constituting in this way, it is possible to achieve a smaller size and higher output of the direct current motor (for example, refer to Patent Document 1).
Also, when the brushes are separated from the segments during rotation of the armature, due to the release of magnetic energy that is stored in the coil, electrical discharge occurs between the brushes and the segment, and thereby electrical noise may occur. For this reason, various techniques have been proposed of providing a condenser or choke coil on the outside or inside of the direct current motor, and reducing the electrical noise by this condenser or coil.
For example, in a direct current motor that realizes a compact size and a flattened shape by arranging a pair of brushes at point symmetrical positions centered on the rotating axis (facing arrangement), the choke coil is arranged in a direction that is approximately perpendicular to the plane at which the brushes are disposed, that is, the choke coil is sterically arranged with respect to the brushes. By doing so, without increasing the size of the direct current motor it is possible to arrange the choke coil in the vicinity of the brushes near the generation source of the electrical noise, whereby reduction of the electrical noise is efficiently achieved.    [Patent Document 1] Japanese Patent No. 3480733    [Patent Document 2] Japanese Patent Application, First Publication No. 2004-56894    [Patent Document 3] Japanese Patent Application, First Publication No. 2004-56895
However, in Patent Document 1, when the permanent magnet is magnetized into four poles, the pair of brushes that make sliding contact with the segment need to be arranged at a 90 degree interval. In this way, when the brushes are arranged at a 90 degree interval, the width of the direct current motor in the radial direction increases. For this reason, although it may become a solution means effective for attaining the downsizing of a direct current motor, there is the problem of it being difficult to become an effective solution means for flattening of a direct current motor.
Also, in the flattened direct current motor as in Patent Document 2 and Patent Document 3, the work involved in assembling a choke coil in a steric manner with respect to the brushes with the above conventional art is extremely difficult, and when production efficiency is taken into consideration, there is the problem of it being difficult to realize in practical terms.
The present invention was achieved in view of the above circumstances, and has as its object to provide a direct current motor that can efficiently achieve flattening.
Also, the present invention provides a direct current motor that can readily attach noise prevention elements such as a condenser and choke coil near the brushes while achieving a small size and flatness.